1. Field of the Invention
The present invention relates to a monitor that tests the conductivity of water.
2. Description of Related Art
Municipal water can contain an unacceptable amount of impurities. Some end users use a reverse osmosis (RO) purification unit to remove the impurities from the water. RO units contain a membrane that captures the impurities while allowing "filtered" water to flow therethrough. Additionally, RO water purification systems may also include a pre-membrane filter and possibly a post-membrane filter to further purify the water. Over time the RO membrane and filters become less effective in removing contaminants from the water. If this condition is not detected and corrected by the replacement of the membrane and/or filter, the water purification unit will become inefficient and the quality of water will decrease to an unacceptable level. It is therefore desirable to have a sensor that can monitor the quality of water in a water purification unit.
U.S. Pat. No. 5,057,212 issued to Burrows discloses a water conductivity monitor for a water purification system. The purification system has a feed water probe within the unfiltered water and a filter water probe within the filtered water of the system. The Burrows monitor includes a button that is coupled to a battery and which provides a voltage to the probes when depressed by an end user. A comparator compares the ratio of the feed water probe voltage and filter water probe voltage, with a threshold value to determine whether the conductivity of the filtered water is below an acceptable level. The output of the comparator is latched into a light emitting diode (LED) to provide an indication of whether the water "passed" or "failed" the test.
The battery in the Burrows monitor is a DC voltage source which will induce electrolysis between the metal surfaces of the probes. Additionally, the probes will function as capacitors that store energy and distort the results of the test. To reduce the "battery" effect of the probes, the Burrows monitor includes a capacitor that creates a reverse flow of current through the probes. Unfortunately electrolysis of the probes still occurs. It would be desirable to provide a water conductivity monitor that does not have the disadvantages of the prior art.